1. Field of the Invention
The invention relates to the bonding of structures such as semiconductor or ceramic devices to one another.
2. Description of the Related Art
The interconnection of semiconductor devices and other structures during the manufacture of circuit chip assemblies typically involves bonding techniques. For example, such techniques include micro-bonding a semiconductor, optical, photonic, ceramic or other element structure to a substrate such as a silicon (Si), indium phosphide (InP) or other substrate to form an electronic or optoelectronic device.
One particular type of bonding is the micro-bonding of optical elements to semiconductor substrates to form an optoelectronic device. For example, it is possible to micro-bond an array of GaAs/AlGaAs optical diodes on a GaAs substrate to a semiconductor substrate such as a Si integrated circuit (IC) chip to form an optoelectronic chip assembly having an arrayed plurality of optical diodes.
In such assembly, each optical diode in the array has a pair of multi-layered, microcontact elements for bonding to a corresponding pair of bonding contacts within an array of bonding contacts on the Si substrate. After solder bumps are formed on one or both arrays of contact elements to be bonded, the structures are aligned, pressed together (tacked) and heated sufficiently to soften or melt the solder bumps for corresponding interconnections to occur. The device formed by the interconnection is then cooled for removal from the bonding apparatus.
However, because of the difference in the respective thermal expansion coefficients of, e.g., the GaAs optical diode array substrate and the Si substrate, mechanical stress often is imparted on the interconnections formed therebetween. Such stress can affect the quality of the interconnections, often resulting in poor quality solder connections or even some ruptures.
In an effort to combat this stress, an encapsulant material typically is applied between the two substrates and allowed to cure prior to final packaging, thus offering some measure of stability to the interconnections. However, any damage to interconnections that occurred prior to encapsulation cannot be repaired.
In cases where the GaAs optical diode array substrate is opaque to the conventional operating wavelength of the optical diodes, the substrate often is removed for proper operation of the device. Such removal is performed, for example, by etching. In such cases, the encapsulant material also protects the interconnections from the etchant in addition to the stability and/or strength provided to the interconnections. For example, see Goossen (U.S. Pat. No. 5,385,632), which is co-owned with this application.
The removal of the GaAs optical diode array substrate (leaving only the array of optical diodes) alleviates most of the mechanical stress within the manufactured optoelectronic device; however, any damage to connections that occurred during previous processing cannot be repaired.
Therefore, despite the stress-reducing-efforts of the encapsulant material and/or the removal of the GaAs optical diode array substrate, the resulting devices typically are still suffering from poor quality bond connections or from ruptures within the multi-layer, micro-contact elements.
Thus, it is desirable to have available a reliable, high yield bonding method that improves upon or overcomes stress-related problems associated with conventional bonding techniques as discussed above.